The underlying premise of the story is great, and the movement from chapter—though quick in pacing—is very good... the story doesn't dwell on something for too long, nor does it bore you. That said, the dialogue is extremely cheesy at the best of times. I can only read through it mostly because it happens during the copious number of sex scenes where such dialogue is... tolerable.
Graphics and animations are very good, though several of the players smile and grin a little too much considering the serious undertones of the underlying story... the MC seems a little too happy at times to be possessed by a demon lord and the serious elf seems a little too giggly considering she's bringing a possessed human and a half-demon to her people that are not particularly fond of possessed anything or half-demons.
Voice acting—there's voice acting!—is only a little stilted at times, which is an improvement over most of the very few developers that reach out to VAs. Most games with voice acted material is usually poorly read to the point I turn off voice audio; imagine my surprise when I actually liked it. The sound effects are really well done and the levels are just right.
Music is usually scene-appropriate and has classical themes, more winds and strings and less horns and percussion. Considering the general theme of the game, I appreciate it.
I haven't quite finished yet, but barring something really going off the rails, I'm going to give this 5 stars. It's good, and so far I definitely recommend it. If I don't come back to edit this, assume it finishes well and give it a shot.